Method of making anhydrous magnesium chlorides



Patented Oct, 20, 1925.

UNITED STATES:

PADI. COT'I'RINGER ANI)l WILLIAM R. COLLINGS, OF MIDLAND, MICHIGAN,ABSIGNORS4 PATENT OFFICE.

T0 THE DOW CHEMICAL COMPANY, 0F MIDLAND, MICHIGAN, A CORPORATION OFMICHIGAN.

METHOD 0F MAKING .ANHYDBOUS MACNESIUM CHDORIDIB.

Application led. March 10, 1921. Serial Fo. 451,199.

To all whom z't may concern.'

Be it known that we, PAUL COTTRINGER and WILLIAM R. CoLLINGs, citizensof the United States, and residents of Midland, county of Midland, Stateof Michigan, have jointly invented a new and useful Improvement inMethods of Making Anhydrous Magnesium Chlorides, of which the followingis a specification, the principle of the invention being hereinexplained, and the best mode in which we have contemplated apf plyingthat principle so as to' distinguish it from other inventions. Thepublished methods for the production of anhydrous magnesium chlo-ride(MgCl2), up to a very recent date at least, will be found very wellsummarized in Gmelin-Krauts Handbuch der anorganischen Chemie (1909) II2, p. 420. In the same connection, the well known dificultiesencountered in the production of the waterfree salt are recited, theprincipal such diiculty being that thc normal heXa-hydrate will melt andform a solution in its Water of crystallization at a relatively lowtemperature, and dehyrationl of the resultant solu-- tion must becarried on at a very slight increase in temperature and with extremecaution if decomposition of the salt is to be avoided. The presentimproved method for the production of the anhydrous salt has as itsobject ,the avoidance of this particular diiculty, and also provides forthe more ready and convenient handling of the material during thepreliminary stages of dehydration; as well as for the economical use ofhydrochloric acid gas which is used to drive off the last remainingwaterof crystallization. .v To the accomplishment of the foregoing andrelated ends the invention then consists of the steps hereinafter fullydescribed and particularly pointed out in the claims, the annexeddrawing and the following description settingr forth in ldetail one modeof carrying out the invention, such disclosed mode constituting,however, but one of various ways in which the principle of the inventionmay be used.

In said annexed drawing Fig. 1 is a more Ior less diagrammatic view ofan improved apparatus suitable for carrying out the partial dehydrationof the material 1n questlon, and Fig. 2 1s a snrnilar vlew of anapplaratus specially designed for carryln out t e final stage ofdehydration',

in whic a current of hydrochloric acid gas is employed, as indicatedabove.

The apparatus as shown in Fig. 1 comprises as its rinci al element ashelf dryer 1, through w 1ch t e material is passed successively fromthe u per to the lower shelves 2 in well un erstood manner by means ofshovels or plows 3 carried on .a rotating shaft 4. The material to betreated is fed into the upper end of the dryer by means of asuitable hoper 5 and is discharged at the lower end) throu h an outlet 6. Likewiseconnectedwith suc lower end of the dryer is a duct 7 through which fluegases or products ofv combustion directly received from a gas or oilburner or from a. furnace burning coal or other solid fuel are admit-tedto the interior of the dryer,

through which they circulate in a general upward direction, finallyescaping lthrough an exit duct 8. Connected with said duct 7 is a valvecontrolled branch d'uct or opening 9, whereby outside air may beadmitted in a regulated amount and mixed withthe` aforesaid liue gasesso as to lower the temperature of the latter when 'admited to the-dryer.The dimensions of the apparatus and the temperature and rate of supplyof the Hue gases thus tempered with outside air regulat-ed so that thehighest temperat re encountered by -the material at the lo er or exitend of the dryer will not rise .abo e 350 6, the transfer of suchportion of the partially dehydrated product being indicated by a line l0with direction arrow only. Where the highest tem erature encountered bythe material is 350 egrees centigrade, as just stated, such partiallydehydrated prod- 'uct will consist mainly of rdihydrate (MgCl2.2I-I,O),which has a fusion point above 360 degrees centigrade, and theamount ofthis product diverted for use in mixing with the normal hexa-hydratewill be approximately one half of t-he latter. lVhere such partiallydehydrated product is mixed in amount approximately as stated, with thenormal hydrate, the mixture may be immediately subjected to atemperature of approximately 115 degrees indicated above as thetemperature of the' heating gases as discharged from the apparatus,without any of the harmful effects that would result. were the normalhydrate by itself subjected to such temperature.

It will be noted that the foregoing procedure is distinguished from thatdisclosed in German Patent No. 51,084, dated March 16, 1889. In thefirst place, in our improved process, :it is not the completelydehydrated chloride that is thus adinixcd with the n'o-rmal hydrate, andin the second place,` in our process, such admixt-ure is simply madewith. both materials in solid formwithout, in other Words, fusing thenormal hydrate, and then stirring in the dihydrate which results in theproduction of a hard cake that requires to be broken up before it can bepassed through the drying apparatus. The anhydrous product is 4toovaluable to warrant its use in any large commercial way for thusadmixing with the normal hydra-te and it apparently was never realizedthat the partially dehydrated product might prove cffective in the samemanner to render the normal salt. amenable to ordin-ary methods ofdrying. K

The portion of partially dehydrated salt, (most if not all in the formofthe dihydrate) that isdelivered from the shelf dryer in excess of thatreturned in thefashiion just described to be passed through a secondtime, is thereupon transferred either continuously or Aintermittently toan externally heated rotary drum dryer 12 for treatment in what may beregarded as a second stage of the process. A current of hydrochloricIacid gas 1s continuously passed through said dryer 12 as it rotates,such gasbeing derived initially from any suitable source. The circuit ofthe gas includes one or more towers through which snlphuric acid ofproper strength is passed, either in the samedirection or counter to thecurrent of hydrochloric -acid gas, so as to remove therefromsubstantially all traces of water. ln the illustrative form of.apparatus lshown in Fig. 2, two such towers 1? are thus included 1n thecircuit 14. through which the hydrochloric acid gas is caused to flow bymeans ot a pump 15, suitable valves being provided whereby .such fiow ofgas can be diverted from one to the other tower 13.215 desired. Asutlicient body of sulphuric acid is kept circulating through theparticular tower that happens to be thus in use and such circulationcontinued until the sulphuric acid reaches a density of approxmately 60degrees B aum, whereupon t-he hydrochloric acid gas is switched to theother tower where lanother portion of sulphuric acidof proper strengthto remove the water from'the. gas is ready to be circulated. Aconcentra-tor 16 is connected with the. pipes 17 whereby the circulationof sulphuric acid is thus maintained in the respective towers 13, sothat such acid |after absorbing the maximum amount of water that adcsirable may be concentrated and the acid then returned foil use-ove;again, as will be readily understood.

The circulation of the hydrochloric acid gas may thus be continued aslong as found necessary to effect the dehydration of any particularhatch of partially dehydrated magnesium chloride in drum 12, or byproriding suitable means for continuously feeding such chloride to andremoving same from said drum, the circulation of the hydrochloric acidgas may be continued indefinitely. Where the chloride is dried inbatches the temperature in said rotary drum 12 will be gradually raisedfrom approximately 200 degrees to approximately 500 degrees centigrade,the higher temperature being necessary to insure the complete drivingoft" of the water of crystallization, while if continuous operation isto be secured the partially dehydrated chloride is introduced at one endof the drum, which end is maintained at the lower temperature justindicated, and such temperature gradually increased lengthwise of thedrum until at its other, discharge .end the higher temperature isreached.

4By means of the foregoing steps and 'apparatus it is possible toprepare anhydrous magnesium chloride at a much lower cost than hasheretofore been possible, the hulk of the water of crystallization beingdriven off by ordinary air drying and only the last stage requiring theuse of hydrochloric acid gas. The latter moreover is used over and overagain without material loss save such as may occur due to leakage andthe like. It will be understood, of course, that the process is notlimited to any precise degree of dehydration being reached at the end ofthe first stage` since hydrochloric acid gas will be effective to removewater of crystallization in excess of two molecules, but the .drying inthe first stage is preferably carried to as near this point ofdehydration as possible for reasons of economy. 1f the process becarried out with the temperature ranges as hereinbefore described, theproduct.. resulting from the first stage will be substantially all-inthe dihydrate form.

Other modes of applying the principle of our invention may be employedinstead of the one explained, change beim.r made as regards the stepsherein disclosed. provided lift) those stated by any ofthe followingclaims or their .equivalents be employed.

We claim:

1. In a method of making anhydrous magnesium chloride, the steps whichconsist in intermixin partially dehydrated magnesium chloride with thenormal hydrated salt, both in solid form, and then directly heating themixture at a temperature sufliciently elevated to drive-off water ofcrystallization.

2. In a method of making anhydrous magnesium chloride, the steps whichcon-- sist in intermixing a quantity of the dihydrate salt with thenormal h drated salt, both in solid form, and then irectl heating themixture at a temperature su ciently elevated to drive oi' water ofcrystallization. 3. In a, method of making anh drous magnesium chloride,the ste s whic consist in intermixing partially ehydrated magnesiumchloridewith the normal h drated salt,

both in solid form, and then 'directly heating the mixture through atemperature range gradually increasing from approxi.

mately 115 to approximately 350 degrees centigrade.I

4. In a method of making anhydrous magnesium chloride, the steps whichconsist in intermixin a quantity of ,the dihydrate salt with the normalh drated salt, both in solid form, and then irectly heating the mixturethrough a temperature range gradually increasmg from approximately 115to approximately 350 degrees centigrade.

5. In a method of making anh drous magnesium chloride, the steps whicconsist in intermixin a quantity of the dihydrate salt with t e normalhydrated sa t,

driving olf water of crystallization from the resulting mixture until itreaches approximately the dihydrate stage, and returning a portion ofthe product for use over again 1n the receding steps.

6. In a method of making anh drous magnesium chloride, the steps whicconsist in vdrivin `ofi' a portion of the water of crystallization fromthe normal hydrated salt by a current of gases of cumbustion, andregulating the temperature of such gases by admixing air at normaltemperature therewith. I

7. In a methbd of making anh drous lnagnesium chloride, the steps whicconsist(in. driving off a portion of the water of crystallization fromthe normal hydrated salt by moving the latter in opposed directionagainst a current of gases of combustion, and re ulating the temperatureof such gases by atnixing air at normal temperature therewith.

8. In a method of making anhydrous magnesium chloride the steps whichconsist in driving ol a portion of the water of crystallization from thenormal h' drated salt by moving the latter in oppose direction against acurrent of gases of combustion, regulating the temperature of such gasesby admixing air at normal temperature therewith, and returning a portionof' the product for use over again in the preceding steps.

Signed at Midland, Mich., this 4th day of March, 1921.

PAUL eo'r'rRiNGi-JR. l WILLIAM R. COLLINGS.

